It is known that many kinds of products in different physical forms are stored within containers from which they are delivered by pumps or valves.
Many types of manually operable pumps are known for externally dispensing, through the operating stem cavity, fluid substances (liquid or creamy) withdrawn from a container in which a pump is mounted; the hollow stem extends to the outside of the pump by passing through a hole provided in a flange forming part of the pump and bounding the pump at one end.
To prevent vacuum forming in the container interior when the fluid is withdrawn from the latter and dispensed by the pump, the pump must be provided with a passageway or aperture enabling atmospheric air to penetrate into the container in order to maintain therein an essentially constant pressure substantially equal to atmospheric pressure.
The passageway is formed between the outer surface of the pump hollow stem and the surface of the flange hole through which the stem passes: such a system presents two important drawbacks, one of which is that the external air which penetrates into the container can deteriorate the characteristics of the fluid substance contained therein, the other being the fact that this fluid can seep or escape to the outside of the container through said pump when the container and pump lie in a horizontal position or with the pump facing downwards from the container.
Another system to dispense the products is by a valve from an aerosol: the products are stored in sealed containers having an internal pressure which is rather high, obtained by the use of pressurized chlorofluorocarbon propellant (now banned) or by pressurized hydrocarbon propellants.